Use a direct include of strings headers in testing/, third_party/, tools/.

third_party/leveldatabase/chromium_logger.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef THIRD_PARTY_LEVELDATABASE_CHROMIUM_LOGGER_H_
 #define THIRD_PARTY_LEVELDATABASE_CHROMIUM_LOGGER_H_
 
 #include <algorithm>
 #include <stdio.h>
 #include "base/format_macros.h"
-#include "base/string_util.h"
+#include "base/strings/string_util.h"
 #include "base/time.h"
 #include "leveldb/env.h"
 
 namespace leveldb {
 
 class ChromiumLogger : public Logger {
  public:
   ChromiumLogger(FILE* f) : file_(f) { }
   virtual ~ChromiumLogger() {
     fclose(file_);
@@ skipping 63 matching lines @@
       break;
     }
   }
  private:
   FILE* file_;
 };
 
 }  // namespace leveldb
 
 #endif  // THIRD_PARTY_LEVELDATABASE_CHROMIUM_LOGGER_H_